Ion was the first assembly shell released for the TI-83+ calculator, and was programmed by Joe Wingbermuehle. The shell was released with an SDK that was designed to be compatible for both the TI-83 and TI-83+, allowing programs written for Ion to be compiled for use on either calculator. As a result, the shell became extremely popular, and gained widespread community use and support; the shell was featured multiple times on ticalc.org, and even won the prestigious Program of the Month (POTM) award. The shell has since been replaced, however, by more feature-rich shells, such as MirageOS and Doors CS.

Prior to Ion and the release of the TI-83+, Joe was the author of SOS, another popular shell for the TI-83.

Documentation

Taken from the readme file:

Installation

Send ion.8xg to your TI-83 Plus or
Send ion.83g to your TI-83.
To send to your calculator using the Graph-Link
software, select [Link|Send To|RAM] for the
TI-83 Plus or [Link|Send] for the TI-83.
Run prgmION.
Now run prgmA any time you want to run Ion. You
may delete prgmION and prgmIONZ if you like. However,
if you plan on sending Ion to someone else's
calculator, you must send those files to properly
install Ion.

Development History

Taken from the version history in the readme file:

Project Started: 19990623
Version 1.0 <> 19990824
TI-83 size: 1746 bytes (less once installed)
TI-83Plus size: 1801 bytes (less once installed)
-First release!
Version 1.1 <> 19991009
TI-83 size: 1741 bytes (1392 once installed)
TI-83Plus size: 1804 bytes (1546 once installed)
-Fixed the bug that caused the TI-83 version to eat
memory if installed more than once.
-Fixed the bug that caused the symbol table to
become corrupt.
-Fixed the problem with ionFastCopy that caused the
screen to become garbled.
-Now clears the graph screen on exit.
-Fixed a bug in the TI-83 Plus version that caused
some crashes.
-Fixed a bug in the TI-83 Plus version that caused
some programs to detect external levels incorrectly.
Version 1.2 <> 19991121
TI-83 size: 1742 bytes (1420 once installed)
TI-83Plus size: 1795 bytes (1571 once installed)
NOTE: This version is not compatible with previous
versions! Reset the RAM before installing by
selecting [2nd] [+] [7] [1] [2] installing.
You may want to save your programs first.
-Fixed a bug that caused some crashes.
-Added the ability to go to the previous list.
Version 1.3 <> 20000101 - Ring in the new year with Ion!
TI-83 size: 1764 bytes (1431 once installed)
TI-83Plus size: 1783 bytes (1549 once installed)
-Y2K OK
-Major improvements to the module code. Forced
restart now works properly and reruns all
modules with keycode 1. Modules now run at the
proper location on the TI-83 (fixes some
crashes). Module detection number changed to
a two (all modules must be reassembled)!
-Improved program detection code; fixes the
reinstall problems that occurred periodically.
Version 1.4 <> 20000103
TI-83 size: 1592 bytes (1375 once installed)
TI-83Plus size: 1725 bytes (1491 once installed)
-Fixed a bug in the TI-83 Plus module code.
-Added another module event: program selection.
Program selection is code 2.
-Now the bottom line of the Ion screen is blank
unless a module is installed. zmInfo, included
in ion.8xg and ion.83g, displays the
standard bottom line.
-Compensated for a bug in the TI-83 Plus ROM
that caused running prgmA to have no effect
sometimes.
-Optimized a little more.
Version 1.5 <> 20000519
TI-83 size: 1535 bytes (1318 once installed)
TI-83Plus size: 1626 bytes (1392 once installed)
-Improved the program loader. Now Ion is much
smaller and more stable.
-Fixed a bug that sometimes caused problems
when running TI-83Plus archived programs.
-Now external levels (for most programs) can
be used from Flash ROM (TI-83Plus). Note that
saving level data does not work when the
level is in Flash ROM.
Version 1.6 <> 20000617
TI-83 size: 1529 bytes (1312 once installed)
TI-83Plus size: 1630 bytes (1396 once installed)
-Fixed the bug in the ionDetect library routine
which caused some programs to crash on the
TI-83 Plus. Unfortunately, this added to the
program size for the TI-83 Plus.
-Shaved off a few bytes here and there.
-The source code is now included.